Determining levels of substances using multistatic probes

ABSTRACT

The disclosed technology pertains to multistatic probes that can determine a level of one or more substances. A multistatic probe can include transmitting and receiving conductive elements that are electrically distinct and which are capable of conveying electromagnetic energy in proximity to/from substances of interest. The conductive elements can be arranged to be adjacent to a coupler that is positioned at a dielectric mismatch boundary between substances of interest, whereby an electromagnetic signal transmitted on the transmitting conductive element causes a change in capacitance in the transmitting conductive element upon the electromagnetic signal traversing a part of the transmitting conductive element substantially adjacent to the coupler, which causes a corresponding electromagnetic signal to be coupled to the receiving conductive element. Attributes of the received electromagnetic signal can be evaluated relative to the transmitted electromagnetic signal to determine a level associated with one or more of the substances of interest.

CLAIM OF PRIORITY

[0001] This application claims priority to and the benefit of UnitedStates Provisional Patent Application No. 60/409,360, filed Sep. 9,2002, the entirety of which is incorporated herein by reference.

RELATED APPLICATIONS

[0002] This is also related to the following co-pending andconcurrently-filed U.S. Utility Patent Application Nos., the entirety ofwhich are incorporated herein by reference:

[0003] 10/_______, “Characterizing Substances With Multistatic Probes,”identified by Attorney Docket No. FOM-139.01; and

[0004] 10/_______, “Measuring Distances Using Multistatic Probes,”identified by Attorney Docket No. FOM-139.03.

TECHNICAL FIELD

[0005] The disclosed technology relates generally to determiningcharacteristics of substances and more particularly to determining suchcharacteristics using multistatic probes.

BACKGROUND

[0006] Detecting the presence and characteristics of particularsubstances and/or combinations of substances that are difficult toinspect can provide entities interested in the control and monitoring ofsuch substances with information critical to those entities' operations.Technology capable of such detection and characterization findsapplicability in many areas, such as in, linear displacement measurementdevices, position measurement, pressure analysis, land mine detection,fluid/soil contamination, fluid/gas level detection, substancecomposition analysis, geological mapping/imaging, and in a myriad ofstorage, monitoring, and processing applications.

[0007] The technologies that have been developed and applied to suchdetection and characterization are as diverse as their applications andinclude, for example, mechanical/electromechanical sensors (e.g.,floats), sonic/ultrasonic sensors, radar (e.g., ground penetratingradar), time domain reflectometry sensors (“TDR”), x-ray sensors,capacitive level sensors, etc. These technologies can exhibitshortcomings that mitigate their usefulness such as, for example, floatsthat can be unreliable particularly in multi-fluid and/or corrosiveenvironments; sonic/ultrasonic sensors whose acoustic signals mayreflect off of foamy material or container walls and fail to capturefluidic surfaces and boundaries; radar sensors may be expensive,complex, bulky, and/or may exhibit limited resolution; TDR sensors mayexhibit excessive ringing and thereby limit short range detection andmay require different designs when used with different dielectricsubstances due to changes in reflection amplitude; x-ray sensors mayfail to differentiate between similar substances; and capacitive levelsensors may not operate accurately due to nonlinear dielectricproperties of a substance and may fail to provide desirable informationabout a particular mixture. Accordingly, entities interested inresidential, commercial, industrial, medical, scientific, military,and/or other applications of substance characterization technology havea continuing interest in further developing these technologies to moreaccurately and flexibly meet their control and monitoring objectives.

SUMMARY

[0008] The disclosed technology can be used in the development andoperation of multistatic sensor probes that can characterize substancesand relationships between substances. A multistatic probe can includetransmitting and receiving conductive elements that are physicallyand/or electrically distinct and which are capable of conveyingelectromagnetic energy to/from a substance of interest. The transmittingand receiving conductive elements can be arranged so as to be in contactwith at least one dielectric mismatch boundary associated withsubstances of interest, whereby an electromagnetic signal transmitted onthe transmitting conductive element causes a correspondingelectromagnetic signal to be conveyed on the receiving conductiveelement in response to the transmitted signal being in proximity to thedielectric mismatch boundary. Attributes of the received electromagneticsignal can be evaluated relative to the transmitted electromagneticsignal to determine one or more characteristics associated with at leastone of the substances forming the dielectric mismatch boundary.

[0009] In one embodiment, the disclosed technology can be used todevelop systems and perform methods in which an electromagnetic signal(exhibiting, for example, an ultra-wideband frequency) is formed andtransmitted by a transmitter via one or more first conductive elementsthat are in contact with one or more dielectric mismatch boundaries,which correspond to transitional surfaces and/or regions associated withsubstances of interest that exhibit different dielectric constants, suchas may be associated with two or more gaseous substances, vacuums,liquid substances, semi-solid substances, and/or solid substances. Anelectromagnetic signal based on the transmitted signal can be coupled toone or more second conductive elements (that can also be in contact withthe dielectric mismatch boundaries) in response to the dielectricmismatch boundary and can be subsequently received by a receiver. The atleast one first and second conductive elements can be arranged to form aparallel conductor transmission line structure, manufactured fromflexible material to enable the conductive elements to substantiallyreform into a desirable shape/configuration, and/or exhibitsubstantially identical cross-sections (e.g., quadrilateral). Aprocessing clement can evaluate attributes (e.g., a time delaydetermined using an equivalent time sampling circuit) of the receivedelectromagnetic signal relative to the transmitted electromagneticsignal to determine characteristics (e.g., level and/or volume of afluid in an above-ground or below-ground storage tank) of one or moresubstances associated with the dielectric mismatch boundary. Theprocessing element can also communicate one or more of the attributes ofthe received electromagnetic signal and/or one or more of thecharacteristics of the substances associated with the dielectricmismatch boundary to a local and/or remote digital data processingdevice during a communication session.

[0010] In one embodiment, a third conductive element connected to aground plane can surround at least part of the at least one first andsecond conductive elements. The at least one first and second conductiveelements can also be positioned substantially parallel to each other andsubstantially perpendicular to the at least one dielectric mismatchboundary.

[0011] In one embodiment, the disclosed technology can include a couplerthat can operate as an electromagnetic shunt path between the at leastone first and second conductive elements and can be positioned at thedielectric mismatch boundary for coupling the received electromagneticsignal independently of the dielectric properties associated with thesubstances forming the dielectric mismatch boundary. The coupler can,for example, exhibit a length corresponding to at least one-quarter of apropagation velocity pulse length of the transmitted electromagneticsignal. A float including a buoyant and/or a weighted component can alsobe provided to position the coupler relative to the at least onedielectric mismatch boundary.

[0012] In one embodiment, the disclosed technology can be used todevelop systems and to perform methods for determining levels and/orvolumes of substances (e.g., fluids) that may be contained in, forexample, above-ground or below-ground storage tanks or other types ofcontainers. A first electromagnetic signal (exhibiting, for example, anultra-wideband frequency) can be formed by a transmitter and conveyed ona first conductive element that is positioned in proximity to one ormore substances. When the first electromagnetic signal traverses a partof the first conductive element that is substantially adjacent to acoupler positioned at a dielectric mismatch boundary (e.g., atransitional surface and/or region between a vacuum, a gaseoussubstance, a liquid substance, a semi-solid substance, and/or a solidsubstance), a resulting change in the capacitance of the firstconductive element can cause a coupling of a second electromagneticsignal (which can be, for example, based on the first electromagneticsignal) to a second conductive element. The amplitude of the secondelectromagnetic signal can be based on the dielectric properties of thecoupler and thus can be independent of the dielectric propertiesassociated with the substances forming the dielectric mismatch boundary.In one embodiment, the coupler can exhibit a length corresponding to atleast one-quarter of a propagation velocity pulse length of the firstelectromagnetic signal. A processor can determine a level and/or volumeof at least one of the substances based at least in part on a time delaybetween the first and second electromagnetic signals that can bedetected by a receiver using, for example, an equivalent time samplingcircuit. The processor can further communicate one or more substancelevels, volumes, and/or other attributes to a local and/or remotedigital data processing device via a data communications network.

[0013] In one embodiment, the first and second conductive elements canbe positioned substantially parallel to each other and substantiallyperpendicular to the dielectric mismatch boundary. In one embodiment,the first and second conductive elements can also be flexible, form aparallel conductor transmission line structure, and/or exhibitsubstantially identical cross-sections (e.g., quadrilateral). In oneembodiment, the disclosed technology can use a float to position thecoupler at the dielectric mismatch boundary. The float can include abuoyant component and/or a weighted component.

[0014] In one embodiment, the disclosed technology can be used todevelop systems and to perform methods for measuring distances betweenpoints of interest that can be associated with one or more objects. Afirst electromagnetic signal (exhibiting, for example, an ultra-widebandfrequency), formed by a transmitter and conveyed on a first conductiveelement, can traverse a part of the first conductive element that issubstantially adjacent to a coupler positioned at a point of interest,thereby resulting in an increase in capacitance between the firstconductive element and a second conductive element along portions ofthese conductive elements adjacent to the coupler. The increasedcapacitance between these portions of the first and second conductiveelements causes a second electromagnetic signal based on the firstelectromagnetic signal to be coupled to the second conductive elementthat is otherwise physically and/or electrically distinct from the firstconductive element. In one embodiment, the coupler can exhibit a lengthcorresponding to at least one-quarter of a propagation velocity pulselength of the first electromagnetic signal. A processor can executeinstructions to determine a distance associated with the point ofinterest based at least in part on a time delay between the first andsecond electromagnetic signals that can be detected by a receiver using,for example, an equivalent time sampling circuit. The distance cancorrespond to, for example, a dimension associated with an object, adisplacement between objects, an angular orientation, and/or a degree ofpressure. The processor can further communicate the distance and/or databased thereon to a local and/or remote digital data processing deviceduring a communication session.

[0015] In one embodiment, the first and second conductive elements canbe flexible, form a parallel conductor transmission line structure,and/or exhibit substantially identical cross-sections (e.g.,quadrilateral). In one embodiment, the disclosed technology can alsoprovide for a supporting material that can slidably receive the couplerin a channel defined therein and this supporting material can maintain aconsistent displacement between the coupler and the first and secondconductive elements.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The foregoing discussion will be understood more readily from thefollowing detailed description of the disclosed technology, when takenin conjunction with the accompanying drawings in which:

[0017]FIG. 1 illustrates exemplary waveforms of electromagnetic signalsthat may be encountered during the operation of multistatic and TDRprobe systems;

[0018]FIG. 2 schematically illustrates exemplary elements of amultistatic probe system;

[0019]FIG. 3 illustrates an exemplary embodiment of a parallel coplanarstrip transmission line that may be used as an element of themultistatic probe system of FIG. 2;

[0020]FIG. 4 illustrates an exemplary methodology that may be preformedduring the operation of the multistatic probe system of FIG. 2;

[0021]FIG. 5 illustrates exemplary waveforms of electromagnetic signalsthat may be encountered during the operation of multistatic probesystems, in the absence of and in the presence of couplers;

[0022]FIG. 6A schematically illustrates an exemplary use of a float, acoupler, and/or a weight with the multistatic probe system of FIG. 2;

[0023]FIG. 6B schematically illustrates exemplary cross-sections of thecoupler of FIG. 6A when used with the transmission line structure ofFIG. 3;

[0024]FIG. 7A schematically illustrates an exemplary embodiment of amultistatic probe system when used as a linear distance measurementdevice; and

[0025]FIG. 7B schematically illustrates an exemplary cross-section ofthe linear distance measurement device of FIG. 7A.

DETAILED DESCRIPTION

[0026] Unless otherwise specified, the illustrated embodiments can beunderstood as providing exemplary features of varying detail of certainembodiments, and therefore, unless otherwise specified, features,components, processes, modules, data elements, and/or aspects of theillustrations can be otherwise combined, interconnected, sequenced,separated, interchanged, and/or rearranged without departing from thedisclosed systems or methods. Additionally, the shapes, sizes, andorientations of elements are also exemplary and unless otherwisespecified, can be altered without affecting the disclosed technology.

[0027] For the purposes of this disclosure, the term “substantially” canbe broadly construed to indicate a precise relationship, condition,arrangement, orientation, and/or other characteristic, as well as,deviations thereof as understood by one of ordinary skill in the art, tothe extent that such deviations do not materially affect the disclosedmethods and systems.

[0028] Time Domain Reflectometry (TDR) refers to a technology that hasbeen applied in the characterization of substances and involvestransmitting an electromagnetic signal on a conductive element (e.g., atransmission line) immersed in or otherwise in contact with a substanceof interest, while simultaneously monitoring the same conductive elementfor corresponding electromagnetic signals that are reflected along theconductive element. A conductive element can be understood to be capableof conveying electromagnetic signals and can be, for example, astructure of substantially constant cross-section. Electromagneticsignals can be reflected along the same conductive element in responseto changes in the conductive element's characteristics (e.g., impedance)that may be affected by substances that are in contact with theconductive element at particular locations along its length.

[0029] For example and with reference to the exemplary waveform 102(labeled as W-TDR) measured on a typical TDR probe in FIG. 1, at leastpart of an electromagnetic signal 104 transmitted on a transmission lineimmersed in a tank or other container containing air and a liquid (e.g.,water) substance will be reflected along the transmission line when theelectromagnetic signal 104 encounters the change in the transmissionline's impedance that occurs above and below the dielectric mismatchboundary between the air and the liquid. The amplitude of the reflectedsignal 106 is related to the difference in impedance (referred to as areflection coefficient) and thus to a difference in the dielectricconstants of the substances forming the dielectric mismatch boundary. Adielectric mismatch boundary can refer generally to a surface or regionbetween substances that exhibit different dielectric constants. Adielectric constant of a substance can refer to a measure of the abilityof that substance to store energy in an electric field relative to thepermittivity of free space and can therefore be used to identify and/orotherwise characterize a substance of interest. Analysis of the timedifferential between the transmitted and reflected electromagneticsignals 104, 106 can be used to determine the location of the dielectricmismatch boundary and can thus, for example, ascertain the level of theliquid in the tank.

[0030] Similarly, substances in contact with the transmission line canchange the velocity of propagation of the electromagnetic signal alongthe transmission line, which can be used to determine not only the levelof the substances, but also their dielectric constants. A velocity ofpropagation can refer to a ratio of the velocity of light to the squareroot of a product of the relative permeability (capability of storingenergy in a magnetic field) and effective dielectric constant (expressedwith respect to an electric field associated with a signal on anon-shielded transmission line) of the transmission line.

[0031] Unfortunately, TDR systems typically exhibit interference (e.g.,ringing, saturation, etc.) that may interfere with thereception/measurement of the reflected signal 106, particularly insituations where the location of the source of the transmitted signal104 is close to the dielectric mismatch boundary, due to concurrentmonitoring of the same transmission line by receiver-side circuitry thatis normally subjected directly to the output of a transmitter-sidecircuit that produced the transmitted electromagnetic signal 104. Forexample, if the location of the transmitter-side circuitry and thedielectric mismatch boundary were such that the reflected signal 106occurred during an interference zone 108, then the relatively smallamplitude of the reflected signal 106 may be insufficient to overcomethe degree of interference and thus the receiver-side circuitry may failto detect the reflected signal 106. Further, the design of a TDRprobe/device may limit the application of that device to specificapplications, thereby reducing the overall useability of the device assubstances, dielectric constants, and other environmental and/oroperational factors are changed.

[0032] The disclosed technology can reduce, if not eliminate, these TDRshortcomings by using electrically-separate transmit and receiveconductive elements. Sensor probes that are constructed with one or moretransmit conductive elements that are electrically-separate from one ormore receive conductive elements will hereinafter be referred to asbeing multistatic.

[0033] In brief overview and with reference to the exemplary waveform110 (labeled as W-Multistatic) measured on a receive conductive elementof an exemplary multistatic probe in FIG. 1, a transmitter of amultistatic probe can produce an electromagnetic signal (not shown) thatis conveyed along the length of a transmit conductive element. When thetransmitted signal encounters a dielectric mismatch boundary formedbetween substances in contact with and/or otherwise adjacent to thetransmit conductive element, a resulting change in the capacitancebetween the transmit conductive element and a receive conductive element(transmit and receive conductive elements are electrically separate)causes at least part of the transmitted signal to be coupled to theelectrically distinct, receive conductive element. Coupling ofelectromagnetic energy between the transmit and receive conductiveelements corresponds to an amount of signal transfer action, expressed,for example, as a coupling coefficient, that is at least partly based onthe spacing and impedances between the transmit and receive conductiveelements in the vicinity of the dielectric mismatch boundary that causedthe coupled signal 112. The coupled signal 112 can be conveyed along thereceive conductive element, which is monitored by a receiver that candetect and further manipulate the coupled signal without substantialinterference caused by the signal transmitted on theelectrically-separate transmit conductive element, thereby resulting inimproved performance relative to traditional TDR techniques and enhanceddetection capabilities, particularly when encountering multipledielectric mismatch boundaries, close distance measurements, and/ordielectric mismatch boundaries formed by substances with similardielectric constants. Those skilled in the art will recognize thatparasitic capacitance between the transmit and receive conductiveelements and circuit impedance mismatches between transmitter andreceiver circuits (for embodiments in which the transmitter and receivercircuits are positioned on a single circuit board and not completelyisolated) can cause a parasitic signal 114 to appear on the receiveconductive element, however the small amplitude of this parasitic signal114 relative to that of the coupled signal 112 does not materiallyaffect the ability of the receiver to detect the coupled signal 112,even in close-in situations where the dielectric mismatch boundary islocated close to the source of the transmitted signal.

[0034] In more detail and with reference to FIG. 2, an entity interestedin monitoring and/or controlling the level, volume, and/or othercharacteristics of one or more substances 202, 204, 206 in an open orclosed container 208 (e.g., above-ground tank, below-ground tank,under-water tank, pressurized tank, and/or any other type of containercapable of storing one or more substances) can, under the control of aprocessor 210, instruct a transmitter 212 to transmit an electromagneticsignal 214 via one or more transmit conductive elements 216 in contactwith one or more substances of interest 202, 204, 206. In oneillustrative embodiment, the transmitted signal 214 can exhibit anultra-wide band frequency. At least part of the transmitted signal 214can be coupled to a receive conductive element 218 in response to thetransmitted signal 214 encountering dielectric mismatch boundaries, suchas the dielectric mismatch boundary 220 associated with substance A 202and substance B 204 and the dielectric mismatch boundary 222 associatedwith substance B 204 and substance C 206. The coupled signal 224returned along the receive conductive element 218 can be received by areceiver 226 and subsequently processed by the processor 210 using atime source 228 to perform, for example, a time comparison analysisbetween the transmitted signal 214 and the received signal 224 that canbe used to ascertain one or more characteristics of the substances ofinterest 202, 204, 206. The processor 210 can also communicate and/ordisplay the substance characteristics on one or more local and/or remotedigital data processing devices 230 via a data communications network230, bus, and/or other type of digital or analog data path.

[0035] A substance 202-206 can refer generally to any type of gaseous,liquid, gel, semisolid, and/or solid matter, as well as, to anysolutions, mixtures, compositions and/or combinations thereof thatexhibit discernable dielectric properties. As discussed above, adielectric mismatch boundary 220, 222 can refer generally to a surfaceor region between substances that exhibit different dielectricconstants. For the purposes of this disclosure, a dielectric mismatchboundary can also refer to a boundary between a total or partial vacuumand a substance.

[0036] A processor 210 can refer to the digital logic circuitry thatresponds to and processes instructions (not shown) that drive digitaldata processing devices 230, multistatic probes 200, transmitters 212,time sources 228, receivers 226, etc., and can include, withoutlimitation, a central processing unit, a micro-controller, an arithmeticlogic unit, an application specific integrated circuit, a task engine,and/or any combinations, arrangements, or multiples thereof.

[0037] The instructions executed by a processor 210 represent, at a lowlevel, a sequence of “0's” and “1's” that describe one or more physicaloperations of a digital data processing device and/or multistatic probesystem 200. These instructions can be pre-loaded into a programmablememory (not shown) (e.g., EEPROM) that is accessible to the processor210 and/or can be dynamically loaded into/from one or more volatile(e.g., RAM, cache, etc.) and/or non-volatile (e.g., FLASH ROM, harddrive, etc.) memory elements communicatively coupled to the processor210. The instructions can, for example, correspond to a) theinitialization of hardware within a digital data processing deviceand/or a multistatic probe system 200, b) an operating system thatenables the hardware elements to communicate under software control andenables other computer programs to communicate, and/or c) softwareapplication programs or other computer programs that are designed toperform particular functions for an entity, such as functions relatingto the operation of the multistatic probe system 200 (e.g., monitor alevel and/or a moisture content of a substance of interest).

[0038] A digital data processing device 230 can be a personal computer,computer workstation (e.g., Sun, HP), laptop computer, server computer,mainframe computer, handheld device (e.g., personal digital assistant,Pocket PC, cellular telephone, etc.), information appliance, or anyother type of generic or special-purpose, processor-controlled devicecapable of receiving, processing, and/or transmitting digital data. Asis known to those skilled in the art, a digital data processing devicecan include a variety of subsystems (e.g., display subsystem, videosubsystem, input/output subsystem, memory subsystem, storage controllersubsystem, network interface subsystem, etc.) and software processes(e.g., operating system, software application programs, database, etc.)executing thereon.

[0039] A local user (not shown) can interact with a processor 210 of amultistatic probe system 200 and/or with a digital data processingdevice 230 in communication therewith by, for example, viewing a commandline, LED display, graphical, and/or other user interface and enteringcommands via an input device, such as a mouse, keyboard, touch sensitivescreen, track ball, keypad, etc. The user interface can be generated bya graphics subsystem of a digital data processing device, which rendersthe interface into an on or off-screen surface (e.g., in a video memoryand/or on a display screen). Inputs from the user can be received via aninput/output subsystem and routed to a processor 210 via an internal bus(not shown) (e.g., system bus) for execution under the control of anoperating system.

[0040] Similarly, a remote user (not shown) can interact with aprocessor 210 of a multistatic probe system 200 and/or with a digitaldata processing device 230 in communication therewith over a datacommunications network 232 (e.g., Internet, intranet, extranet, localarea network, metropolitan area network, wide area network, radiofrequency modem, etc.). The inputs from the remote user can be receivedand processed in whole or in part by a remote digital data processingdevice collocated with the remote user. Alternatively or in combination,the remote user's inputs can be transmitted back to and processed by theprocessor 210 and/or by the digital data processing device located inproximity thereto via one or more networks using, for example, thinclient technology. The user interface of the local digital dataprocessing device can also be reproduced, in whole or in part, at theremote digital data processing device collocated with the remote user bytransmitting graphics information to the remote device and instructingthe graphics subsystem of the remote device to render and display atleast part of the interface to the remote user.

[0041] Network communications between two or more processors and/ordigital data processing devices typically require a network subsystem(as embodied in, for example, a network interface card, a modem, asatellite data modem, etc.) to establish one or more communicationsessions between the processors/devices. A communication session canrefer to a series of interactions between two or more processors/devicesand/or other types of communication end points that occur during thespan of a connection and can require the use of multiple elements of adata communications network, a point to point connection, a bus, awireless transceiver (e.g., radio frequency modem) and/or any other typeof digital and/or analog data path capable of conveyingprocessor-readable data.

[0042] A data communications network 232 can comprise a series ofnetwork nodes (e.g., the processor 210, a local digital data processingdevice, and/or a remote digital data processing device 230) that can beinterconnected by network devices and communication lines (e.g., publiccarrier lines, private lines, satellite lines, etc.) that enable thenetwork nodes to communicate. The transfer of data (e.g., messagespertaining to characteristics of substances of interest 202-206) betweennetwork nodes can be facilitated by network devices, such as routers,switches, multiplexers, bridges, gateways, etc., that can manipulateand/or route data from a source node to a destination node regardless ofany dissimilarities in the network topology (e.g., bus, star, tokenring), spatial distance (local, metropolitan, or wide area network),transmission technology (e.g., TCP/IP, Systems Network Architecture),data type (e.g., data, voice, video, or multimedia), nature ofconnection (e.g., switched, non-switched, dial-up, dedicated, orvirtual), and/or physical link (e.g., optical fiber, coaxial cable,twisted pair, wireless, etc.) between the source and destination networknodes.

[0043] As known to those of ordinary skill in the art, a transmitter 212(also referred to as transmitter-side circuitry) can refer to digitaland/or analog circuitry that can receive instructions from and providestatus to a processor 210 (via, for example, a digital-to-analog oranalog-to-digital converter), form one or more electromagnetic signals214 at a frequency and amplitude specified by the processor 210, and/ortransmit the electromagnetic signals 214 along one or more transmitconductive elements 216. In one illustrative embodiment, the transmitteruses clock signals (which can exhibit, for example, a frequency range ofbetween about 2 MHz to 8 MHz, such as a square-wave at 3.665 MHz)received from a pulse rate frequency clock in the time source 228 toperform at least some of its operations.

[0044] As known to those of ordinary skill in the art, a receiver 226(also referred to as receiver-side circuitry) can refer to digitaland/or analog circuitry that can receive instructions from and providestatus and/or signal information to a processor 210 (via, for example, adigital-to-analog or analog-to-digital converter), and/or amplify,filter, and digitally sample the return signal 224 received via thereceive conductive element 218.

[0045] As known to those of ordinary skill in the art, a time source 228can refer to digital circuitry that can, for example, provide a pulserate, variable-delayed frequency clock that operates on an equivalenttime sampling detector that may be contained within a receiver 226 andwhich can detect and/or be used to construct a representation of thereceived signal 224. In one illustrative embodiment, the time source 228can include a delay controller, such as a voltage integrator op-amp rampcircuit with capacitor discharge reset to produce a precise linear timeramp for the delay circuit.

[0046] As known to those of ordinary skill in the art, transmit andreceive conductive elements 216, 218 can refer to structures capable ofconveying electromagnetic energy, such as coaxial-arranged conductors,dielectric rods, microstrip lines, coplanar striplines, coplanarwaveguides, etc. The transmit and receive conductive elements 216, 218can also form a parallel conductor transmission line structure. Althoughthe multistatic probe is illustrated with the transmitter 212 andreceiver 226 connected to corresponding ends of the transmit and receiveconductive elements 216, 218, those skilled in the art will recognizethat the transmitter 212 and receiver 226 can also be applied toopposite ends of their respective conductive elements 216, 218 to, forexample, measure a velocity of propagation associated with one or moresubstances 203, 204, 206.

[0047] Similarly, the transmit and receive conductive elements 216, 218are illustrated in FIG. 2 as exhibiting substantially the samecharacteristics (e.g., length), but those skilled in the art willrecognize that their width, length, orientation, or othercharacteristics can vary. In one embodiment, the characteristics of thetransmit and receive conductive elements 216, 218 can be varied, whiletheir transmission line impedance remains substantially constant. Inanother embodiment, their characteristics can be varied according to apredetermined arrangement for impedance matching and/or to obtain adesirable signal response (e.g., a coupled return at a predeterminedpoint on the probe that can serve as a point of reference). For example,the receive conductive element 218 can extend to different depths in thetank 208 containing the substances of interest 202-206 than theillustrated transmit conductive element 216 (or vice verse), thetransmit and receive conductive elements 216, 218 can be substantiallyparallel and equidistant and/or they can exhibit different orientations,the transmit and receive conductive elements 216, 218 can besubstantially perpendicular to the dielectric mismatch boundaries 220,222 or they can exhibit other angular offsets, the transmit and receiveconductive elements 216, 218 can exhibit substantially identicalcross-sections (e.g., quadrilateral) or they can exhibit differentcross-sections, and/or at least part of the transmit and/or receiveconductive elements 216, 218 can be shielded or unshielded, terminatedor unterminated, etc.

[0048] Further and although only a single transmit conductive element216 and a single receive conductive element 218 are shown in FIG. 2 toretain the clarity of the figure, those skilled in the art willrecognize that more than one transmit conductive element 216 and receiveconductive element 218 can be provided. In one embodiment, a plurality(e.g., two or more) of transmit conductive elements 216 and receiveconductive elements 218 can be connected to a single transmitter 212 anda single receiver 226, respectively. In another embodiment, a pluralityof transmit conductive elements 216 and receive conductive elements 218can be connected to more than one transmitter 212 and more than onereceiver 226, respectively. In one embodiment, a multistatic probe 200can include a third conductive element (not shown) that substantiallysurrounds at least part of the transmit and receive conductive elements216, 218 and which can function as an electromagnetic shield, mechanicalwear protection, and/or as a stiffening/strengthening member for theoverall probe 200. In one embodiment, the third conductive element canbe connected to a ground plane associated with, for example, thereceiver 226.

[0049] In one illustrative embodiment and with reference to FIG. 3, amultistatic probe 200 can include a parallel coplanar strip transmissionline with an insulating spacer 302 that can maintain a substantiallyequidistant position between a transmit conductive element 216 and areceive conductive element 218. The insulating spacer 302 and transmitand receive conductive elements 216, 218 can be composed of materialsthat are non-absorptive and that are resistant to chemicals,temperature, and material build-up on their surfaces and can therebymaintain an effective dielectric constant. The material forming theinsulating spacer 302 and transmit and receive conductive elements 216,218 can also be selected to exhibit flexible properties (e.g., withcomparatively minor shape memory) that can withstand rolling, folding,kinking, etc., so that the spacer 302 and conductive elements 216, 218reform into their original shapes upon cessation of the forces thatcaused their deformation. For example, the insulating spacer 302 can becomposed of polytetrafluoroethylene (manufactured using, for example, alamination process), fluorinated ethylenepropylene (manufactured using,for example, a co-extrusion process), a polyimide, such as Teflon orKapton (manufactured using, for example, a co-extrusion process), andthe transmit and/or receive conductive elements 216, 218 can be made ofstainless steel (e.g., type 304 or 316).

[0050] In one embodiment, the insulating spacer 302 can be provided inthe form of a laminated tape or film that can substantially surround atleast part of the transmit and receive conductive elements 216, 218. Inone particularly advantageous embodiment, the transmit and receiveconductive elements 216, 218 can be approximately 0.1 inches wide and0.004 inches thick and the insulating spacer 302 substantiallysurrounding at least part of the transmit and receive conductiveelements 216, 218 can fixedly space the conductive elements 216, 218 byabout 0.305 inches with an approximate overall width and thickness ofthe resulting spacer-conductor assembly 304 of 0.5 inches and 0.025inches, respectively. Those skilled in the art will recognize that the“flat” conductive elements and high quality dielectric exhibited by theinsulating spacer of this particular illustrative embodiment can resultin comparatively low signal loss, reduced levels of cross-talk betweenconductive elements, substantially constant impedance that can reducethe attenuation and dispersion of an electromagnetic signal, and/orimproved sensitivity to a dielectric mismatch boundary.

[0051] In one embodiment, at least part of an end of thespacer-conductor assembly 304 can be attached to a weight that may beuseful in maintaining a desired configuration of the assembly 304. Forexample, the weight can be a corrosion resistant element that maintainsthe spacer-conductor assembly 304 in a substantially vertical positionand/or the weight can include a magnet that anchors the end of thespacer-conductor assembly 304 to a desired location within a container208 storing the substances of interest 202-206, such as on a bottom or awall of the container 208.

[0052] In an illustrative operation and with reference to FIGS. 2 and 4,a processor 210 can instruct a transmitter 212 to form anelectromagnetic signal of interest. In response to the processorinstructions, the transmitter 212 can access a pulse rate frequencyclock associated with a time source 228 to form an electromagneticsignal 214 exhibiting the attributes (e.g., amplitude and frequency)specified by the processor 210 and can transmit such signal 214 on atleast one first conductive element 216 (402). In another embodiment, theprocessor does not specify attributes of the electromagnetic signal 214,but rather instructs/triggers other circuitry to form theelectromagnetic signal 214 and/or performs timing measurements onsignals conditioned and/or filtered by other circuitry.

[0053] When the transmitted signal 214 (e.g., one or moreelectromagnetic pulses exhibiting, for example, an ultra-wide bandfrequency) encounters one or more regions of the first conductiveelement that is/are in contact with, and/or otherwise adjacent to, oneor more dielectric mismatch boundaries 220, 222, a change in thecapacitance of the first conductive element 216 relative to a secondconductive element 218 couples at least part of the transmitted signal214 to one or more second conductive elements 218. Under the control ofthe processor 210, the coupled signal 224 (e.g., one or moreelectromagnetic pulses exhibiting, for example, an ultra-wide bandfrequency) that is based on/excited from the transmitted signal 214 canbe sampled by the receiver 226 using a controlled time delay of thepulse rate frequency clock of the time source 228 to form arepresentation of the coupled signal 224 (404). The coupled signaland/or the representation of the coupled signal can also be amplified toincrease the amplitude of the signal and/or filtered to remove harmonicsand other interfering signals, such as signals from parasitic couplingbetween the transmitter and receiver-side circuitry located on a commonprinted circuit board, signals coupled from reflections on the firstconductive element 216, etc. (406).

[0054] The amplified and filtered return signal can be processed by theprocessor 210 and/or receiver 226 relative to the transmitted signal 214to determine attributes (e.g., a time delay) that can be used to derivecharacteristics (e.g., level and/or volume of a substance) associatedwith the substances 202-206 that formed the dielectric mismatch boundary220, 222 (408). The processor 210 can subsequently transmit and/orotherwise communicate the attributes of the return signal and/or thecharacteristics of the substances 202-206 to an interested entity, suchas to a local digital data processing device, a remote digital dataprocessing device 230, an LED display, a computer program, and/or to anyother type of entity capable of receiving the attribute and/orcharacteristic information (410).

[0055] Those skilled in the art will recognize that, even with theenhanced performance of the multistatic probe 200 discussed above, itmay be difficult to characterize adjacent substances that exhibitsimilar dielectric constants, where such conditions could result in, forexample, a relatively low amplitude in the coupled signal 224, and/orwhere the transmit-to-receive time between the transmitted signal 214and coupled signal 224 is comparatively small (which may, for example,experience interference from parasitic coupling). Accordingly andoptionally, the disclosed technology can include a coupler composed atleast in part of a material exhibiting a comparatively high dielectricconstant (e.g., ceramics, plastics, etc.), conductive properties (e.g.,metals, metallized materials, ferrites, etc.), and/or other propertiesthat can be positioned at the dielectric mismatch boundary and that cancreate a coupled return signal 224 of substantially consistentattributes (e.g., amplitude), which is independent of the dielectricproperties of the substances forming the dielectric mismatch boundary.

[0056] For example and with reference to an exemplary waveform 502,measured on a receive conductive element of an exemplary multistaticprobe that traverses a dielectric mismatch boundary formed betweensubstances with similar dielectric constants (e.g., air and mineraloil), in FIG. 5, the amplitude of a coupled signal 504 excited on thereceive conductive element can be low relative to that of acorresponding transmit signal conveyed on a transmit conductive elementand, thus, it may be difficult for a receiver to detect the coupledsignal 504 (particularly in close-in situations where the coupled signal504 may be partially obscured by a parasitic signal 506, as previouslydescribed). As shown in waveform 508, a coupler positioned at the samedielectric mismatch boundary results in a coupled signal 510 that isindependent of the dielectric constants of the substances forming thedielectric mismatch boundary and can therefore result in a higheramplitude relative to that of the coupled signal 504 when a coupler isnot used. Accordingly, the likelihood that the receiver will be able todetect the coupled signal 510 is improved and the enhanced signalstrength of the coupled signal 510 is also less likely to be obscured bya parasitic signal 512.

[0057] With reference to FIG. 6A, one or more couplers 602 can beattached to one or more floats 604 (forming, for example, one or morefloat-coupler assemblies), which can enable the couplers 602 to slidablymove along the transmit and/or receive conductive elements 216, 218 andbe positioned at substantially the same locations as dielectric mismatchboundaries 220, 222 formed between substances of interest 202-206. Anelectromagnetic signal 214 transmitted along the transmit conductiveelement 216 can induce and/or excite a coupled electromagnetic signal224 on the receive conductive element 218 upon traversing that sectionof the transmit conductive element 216 in close proximity to the coupler602, as previously discussed. Since the amplitude of the coupled signal224 is based at least in part on the relatively high dielectricproperties of the coupler 602 located at a dielectric mismatch boundary220, 222 and not on the dielectric properties of the substances ofinterest 202-206 forming such boundary 220, 222, the coupled signal 224can still be considered to be based on a location of the dielectricmismatch boundary 220, 222. Those skilled in the art will recognize thata more accurate determination of the location of the dielectric mismatchboundary 220, 222 can be obtained by also correcting for the velocity ofpropagation changes of the signals 214, 224 caused by the difference inthe dielectric constants of the substances 202-206.

[0058] Those skilled in the art will recognize that the properties(e.g., density, viscosity, etc.) of the substances of interest 202-206can be used to determine the buoyant properties and othercharacteristics (e.g., size, shape, etc.) of a float-coupler assembly(may also include an optional weight 606 connected to the float-couplerassembly or transmit/receive conductive elements 216, 218), which can beused to select a particular float-coupler assembly, such that thecoupler 602 can be positioned at substantially the same location as adielectric mismatch boundary 220, 222. Although the coupler 602 is shownas having a length identical to that of the float 604, those skilled inthe art will recognize that the coupler 602 can have a length that isgreater or smaller than that of the float 604. In one embodiment, thecoupler 602 can have a length that corresponds to at least one-quarterof a pulse length of the transmitted signal 214.

[0059] With reference to FIG. 6B, a coupler 602, such as a metallicsleeve, can exhibit a quadrilateral, circular, oval, U-shaped, parallelsegment, and or other shaped cross-section that can form a channelcapable of accepting the spacer-conductor assembly 304 shown in FIG. 3and/or other types of spacer-conductor assemblies. In one illustrativeembodiment, the float-coupler assembly can be formed by stackingstainless steel sheets with quadrilateral channels defined therein andinserting the stacked sheets into a closed-cell, Buna-N, Nitrol rubberfloat, where the quadrilateral channels are dimensioned to providesufficient clearance so that the float-coupler assembly can move freelyalong the spacer-conductor assembly 304 (FIG. 3) inserted therethrough.Those skilled in the art will also recognize that a float 604 with aninternal channel whose walls exhibit a similar conductive path, such asa metal passage in a metal float, can be used in place of, or inaddition to, the coupler 602.

[0060] As discussed herein, the disclosed technology can be used todevelop a variety of measurement devices that can measure, for example,levels and other characteristics of substances stored in a container;the dimensions of an object; a distance between objects; an angularorientation; a position of a hydraulic cylinder, a degree of compressionof a spring in a weight measuring device, a displacement of a bellows ordiaphragm in a pressure measuring device; and/or other types of devicesthat can exhibit changing states.

[0061] In one illustrative embodiment and with reference to FIG. 7A, thedisclosed technology can be used to develop a measurement device 702capable of measuring linear distances associated with one or moreobjects 704 by, for example, aligning one or more movable couplers 602with the positions of interest on the object(s), transmitting anelectromagnetic signal 214 on a first conductive element 216, receivingone or more coupled electromagnetic signals 224 on an at least oneelectrically separate second conductive element 218 in response to thetransmitted signal 214 traversing those sections of the transmitconductive element 216 in close proximity to the couplers 602, andevaluating the attributes of the coupled signals 224 relative to thetransmitted signal 214 to determine a distance 706 between the positionsof interest.

[0062] With reference now also to FIG. 7B, the measurement device 702can include one or more transmit and receive conductive elements 216,218 positioned and/or otherwise integrated within a plastic or othersuitable supporting material 708, which may be at least partiallysurrounded by a third conductive element 710 that may be connected to aground plane and/or provide strength/rigidity to the measurement device702. The supporting material 708 can include a channel 712 definedtherein in close proximity to the transmit and receive conductiveelements 216, 218 and adapted to receive the slidably movable couplers602.

[0063] Although the disclosed technology has been described withreference to specific embodiments, it is not intended that such detailsshould be regarded as limitations upon the scope of the invention,except as and to the extent that they are included in the accompanyingclaims.

What is claimed is:
 1. A system for determining a level of a substance,the system comprising: a first conductive element conveying a firstelectromagnetic signal in proximity to a plurality of substances; acoupler positioned at a dielectric mismatch boundary between thesubstances, the coupler causing a change in a capacitance of the firstconductive element upon the first electromagnetic signal traversing apart of the first conductive element substantially adjacent to thecoupler; a second conductive element conveying a second electromagneticsignal based on the first electromagnetic signal and being coupledthereto by the change in capacitance of the first conductive elementcaused by the coupler; and a processor executing instructions todetermine a level of at least one of the substances based at least inpart on a time delay between the first and second electromagneticsignals.
 2. The system of claim 1 wherein the first and secondconductive elements are positioned substantially parallel to each otherand substantially perpendicular to the dielectric mismatch boundary. 3.The system of claim 1 wherein the first electromagnetic signal exhibitsan ultra-wideband frequency.
 4. The system of claim 1 wherein thedielectric mismatch boundary corresponds to a transitional regionbetween a gaseous substance and a liquid substance.
 5. The system ofclaim 1 wherein the dielectric mismatch boundary corresponds to atransitional region between at least two of a vacuum, a gaseoussubstance, a liquid substance, a semi-solid substance, and a solidsubstance.
 6. The system of claim 1 further comprising a transmitter forforming the first electromagnetic signal.
 7. The system of claim 1further comprising a receiver for detecting the time delay between thefirst and second electromagnetic signals.
 8. The system of claim 7wherein the receiver includes an equivalent time sampling circuit. 9.The system of claim 1 wherein the first and second conductive elementsform a parallel conductor transmission line structure.
 10. The system ofclaim 1 wherein the first and second conductive elements are flexible.11. The system of claim 1 wherein the first and second conductiveelements exhibit quadrilateral cross-sections.
 12. The system of claim 1wherein the first and second conductive elements exhibit substantiallyidentical cross-sections.
 13. The system of claim 1 wherein an amplitudeof the second electromagnetic signal is substantially independent ofdielectric properties associated with the substances forming thedielectric mismatch boundary.
 14. The system of claim 1 wherein thecoupler exhibits a length corresponding to at least one-quarter of apropagation velocity pulse length of the first electromagnetic signal.15. The system of claim 1 further comprising: a float for positioningthe coupler at the dielectric mismatch boundary.
 16. The system of claim15 wherein the float includes a buoyant component and a weightedcomponent.
 17. The system of claim 1 wherein the level corresponds to avolume of fluid in an above-ground storage tank.
 18. The system of claim1 wherein the level corresponds to a volume of fluid in a below-groundstorage tank.
 19. The system of claim 1 wherein the processorcommunicates the substance level to a digital data processing deviceduring a communication session.
 20. A method of determining a level of asubstance, the method comprising: transmitting a first electromagneticsignal on a first conductive element, the first conductive element beingin proximity to a plurality of substances; providing a couplerpositioned at a dielectric mismatch boundary between the substances, thecoupler causing a change in a capacitance of the first conductiveelement upon the first electromagnetic signal traversing a part of thefirst conductive element substantially adjacent to the coupler;receiving a second electromagnetic signal based on the firstelectromagnetic signal at a second conductive element and in responsethe change in capacitance of the first conductive element caused by thecoupler; and determining a level of at least one of the substances basedat least in part on a time delay between the first and secondelectromagnetic signals.
 21. The method of claim 20 wherein the firstand second conductive elements are flexible.
 22. The method of claim 20wherein the first and second conductive elements are positionedsubstantially parallel to each other and substantially perpendicular tothe dielectric mismatch boundary.
 23. The method of claim 20 wherein anamplitude of the second electromagnetic signal is independent ofdielectric properties associated with the substances forming thedielectric mismatch boundary.
 24. The method of claim 20 furthercomprising: providing a float for positioning the coupler relative tothe dielectric mismatch boundary.